Method of refining paraffin waxes



Dec. 15, 1942. H. J. MOYER 2,305,024

METHOD OF REFINING PARAFFIN WAXES 'Filed Nov. 30, 1940 PAN JWEATER.

Patented Dec. 15, 1942 METHOD OF REFI NIN G PARAFFIN WAXES Harold J.Moyer, Summit, N. J., assignor to Standard Oil Development Company, acorporation of Delaware Application November 30, 1940, Serial No.367,940

Claims.

Ihe present invention relates to the refining of 'parafiin waxesobtained from petroleum or other mineral oil sources. The invention isespecially concerned with improvements in the so-called sweatingoperations in which the final amounts of oily constituents are removedfrom the waxy constituents. In accordance with the present invention,improvements in sweating operations are secured by charging the sweatingapparatus with presolidified crude wax instead of with molten crude Wax.When operating in this manner, the efficiency and capacity of a sweatingapparatus is materially increased, since it is no longer necessary tosolidify the molten wax in the sweater apparatus. A preferred adaptationof my invention utilizes a cooling fluid by which a relatively small waxparticles size is secured.

The cooling fluid also functions as a carrier medium for charging thetrays of the sweating apparatus in a manner to secure a uniform and evendistribution of the small solid wax particles.

It is well-known in the art to separate waxy constituents from petroleumoils by various processes and to refine the crude separated waxes bysubjecting them to carefully regulated heat treatment, usually in asweater house. Separation of the waxy constituents from a feed oil byconventional method usually comprises chilling the waxy feed oil to atemperature at which the wax crystallizes and passes out of solution,followed by filtering the chilled mixture. The waxes so obtained usuallyretain appreciable amounts of the oily constituents, the concentrationof which may vary from about 10% to 50% or more based upon the oily wax.These waxes, due to the amount of oil present, are semi-solid andunctuous in nature, particularly so when the amount of oil present isrelatively high. The slack wax cake is removed from the filter press,melted in a suitable receptacle and then conveyed in a molten state tosweating apparatus, the conventional form of which comprises amultiplicity of shallow metal pans stacked one above the other. Each panis equipped with a false, perforated bottom and a continuous coil ofpipe through which a heating or cooling fluid may be circulated. Thestack of pans is closed within the building, commonly known as a sweaterhouse. The usual practice, in charging the sweater pans, is to fill eachpan with water to the age receptacles.

height of the false bottom which is withdrawn from the bottom of the panafter the wax charge has solidified. The molten wax is then charged tothe pan in such a Way that it floats upon the Water and so that theinterface between the wax and oil is in contact with the perforatedplate. Under these conditions the pipe coil which is disposedimmediately above the false bottom is submerged in the wax.

The molten wax is solidified by circulating cooling water or anequivalent cooling medium through the coil, and by means of cool airwhich is passed through the sweater house. After the crude wax issolidified, it is sweated and the oily constituents removed by graduallyraising the temperature or" the oil-wax cake by circulating a heatedfluid in the submerged coil and heated air within the sweater house. Asthe temperature of the crude wax cake rises, the oily constituents arefirst removed. After removal of an appreciable amount of the oilyconstituents, waxes of gradually increasing melting points areremoved.These waxes contain gradually diminishing percentages of oil as thesweater house temperature and the melting points of the fused waxesincrease. Finally, the sweating operation progresses to the point whereonly the porous structure of the highest melting point wax remains inthe solid state on the perforated false bottom since the other waxfractions have melted out and have been drained off by grades to stor-The remaining solid, relatively high melting point wax is substantiallyoil-free and is known in the art as crude scale wax. Crude scale waxcontains approximately 2% of oil based upon the wax and is hard andfirm, and generally possesses some discoloration. This crude scale waxis generally subjected to further refining and sweating in order toremove the remainder of the oil by methods similar to those describedabove for slack wax sweating except for some variations in temperaturesemployed for the fractional fusion of the crude scale wax. This methodfor refining waxes is applicable to waxes obtained by any manner such asthose obtained when using dewaxing solvents of the character of propane,various ketones, and the like. Thismethod of refining waxes possesses. adistinct disadvantage that an appreciable time period required in orderto solidify the wax,

which may amount to 14 hours or more. That this factor is critical isapparent when it is considered that a cycle of this character mayrequire about 27 hours or so.

In conventional wax-sweating operations, the crude oil containing wax ischarged to the sweating apparatus pans in liquid form and there cooledand solidified. This materially limits the capacity of the sweatingapparatus by appreciably increasing the time cycle. In order to shortenthe time cycle, Various suggestions have been made that the time periodnecessary for solidifying the wax be eliminated by charging the waxdirectly to the trays in the solid form. However, suggestions heretoforemade of this character have not been successful due to the fact that thewaxes removed from the filters, centrifuges, or plate and frame pressesare irregular and lumpy in form, and thus cannot be readily transferredto the sweater pans. Furthermore, practice has demonstrated that waxeswhich are relatively large in form, or in which the wax particles areirregular in size cannot be successfully sweated.

,I-Iowever, I have now discovered a process by which, wax may be chargedto the sweaters in solid form in an efficient and economical manner andby which it is possible to sweat the solid wax in a manner to secureresults superior to the resultssecured when. sweating wax charged to thesweaters "in the liquid state. By operating in a manner which eliminatesthe solidification period from the sweater apparatus cycle, theefficiency 7 of the sweaters can be greatly increased and the capacityof same more than doubled. My invention entirely eliminates thesolidifying and cooling period which is required when charging thesweaters by the conventional method. In accordance with the presentinvention, the oily wax cake as it is removed from the filters,centrifuges, plate and frame presses or ,aprior sweater is handled in amanner to secure vwax particles having a uniform relatively small sizewhich are then charged to the sweater. Wax particles of this characterare preferably secured byintermittently ejecting the wax from amultiplicity of suitable relatively small apertures in the form of smallpellets or globules into a stream of cold Wateror an equivalent coolingfluid. In accordance with the preferred modi- I lficatijon of thepresent invention, this cooling fluid also functions as a carrier mediumfor introducing the small solid Wax particles into the sweating trays. Vi

operating in this manner, utilizing the cooling fluid as the carriermedium, the small. wax particles are distributed uniformly and evenlyever the wax trays to the desired height. The cooling fluid, preferablywater, is allowed to drain from the pan after distributing the waxparticles on the tray. In this manner any desired depth of crude wax,limited only by the "height of the sidewalls, may be readily attained oneach tray. The cooling fluid after removal from the tray may be cooledand recycled, or discarded as desired. After the cooling fluid isremoved from the tray, the sweating operation may be immediately startedby gradually raising the temperature of the solid small wax particles.

The process of my invention may be readily understood by reference tothe attached drawing'illustrating modifications of the same. Fig- "ure'1' illustrates a diagrammati'cal flow plan of a "conventional sweatingoperation adapted in "accordance with the present invention. Figuresired size.

2 illustrates in some detail a sweater tray, while Figures 3 and 4illustrate preferred modifications of securing the relatively smallsolid wax particles.

Referring specifically to Figure 1, it is assumed that the crude,oil-containing wax fractions have been secured from conventionaldeoiling operations. The crude wax fraction is melted in vessel I bymeans of steam pipe coil 2. Liquid wax is withdrawn from vessel I bymeans of line 3 and pump 4 and is ejected at point A into a stream ofcold water by means of an ejector arrangement ii. The water is withdrawnfrom water storage 6 by means of pump I and is introduced into ejectorarrangement 5 by means of line 8. Beyond point A the ejected waxes alongwith the water flow upwardly through ejector arrangement 5 underconditions whereby the ejected wax particles tend to form sphericalpellets. The solid wax particles and water are withdrawn from ejectorarrangement 5 by means of line 9 and passed to trays or pans ll! of thesweater apparatus I I. The water utilized in conveying the wax functionsto distribute the wax uniformly into pans I0. After the pans Ifi havebeen filled to the desired depth with the wax pellets, the water isdrained from the respective pans by means of withdrawal line I2controlled by valves iii. The wax pellets are retained in the pans bymeans of the perforated bottom plates Id. The cooling carrier fluidwhich comprises water and which is withdrawn from sweater apparatus IIby means of line I2 is passed through cooler I5 and recycled to waterstorage 4 by means of line I6.

Figure 2 illustrates in some detail a pan or tray arrangement I0,Carrier fluid containing the solid wax particles is introduced by meansof line 9 and the fluid Withdrawn by means of line I2 controlled bymeans of valve IS. The solid wax particles are retained on the tray bymeans of perforated plate I4. After the removal of the carrier andcooled fluid the sweating operation is started and controlled by meansof heat which is introduced into pans ID by means of a heating fluidconducted through coil ll and then withdrawn.

Figure 3 illustrates in some detail ejecting ,arrangement 5. Water isintroduced into ejecting arrangement 5 by means of line v8 while themolten wax is introduced by means of line 3. A suitable cuttingarrangement 20 powered in any desirable manner is provided for securingthe desired pelleted size. The arrangement shown for the purposes ofillustration comprises an apparatus which is provided with anoscillatory motion which cuts the extruded wax to the de- Figure 4illustrates the cutting arrangement 20 in some detail. Cuttingarrangement 20 is provided with an oscillating cap 2| which opens andcloses a series of apertures through which the molten wax is protrudedin a manner to cut the molten wax to the desired particle size.

7 The present invention may be widely varied. The size of the waxpellets may vary considerably and in general is of such a diameter thatthey may be readily carried along with the cooling fluid and may bereadily sweated. However, in order to secure rapid solidification of thewax on contact with the water, it is preferred that the'diameter of theparticles be less than /2 inch.

I have found that particularly desirable results aresecured when thediameter of the wax particles is in the range from about V8 to inch.

If the wax particles are too small, emulsions tend to form which impairthe sweating process, hinder separation of oil from wax, and decreasethe oil-free wax yield from a given oil-wax mixture. If the waxparticles are too large, they are difficult to handle in the describedmanner. Furthermore, non-uniform sweating also results.

It is to be understood that the oil-containing crude wax may be ejectedinto the stream of cooling fluid either as a liquid or as a plasticsolid. When the wax is ejected into the cooling fluid as a liquid, thecrude wax will be both solidified and cooled by the cooling fluid.However, when the wax is ejected as a solid, heat may or may not beremoved and will depend upon the relative temperatures of the extrudedwax and the cooling fluid. When solid wax is ejected into the water oran equivalent cooling fluid, it is preferably accomplished by anextrusion means known in the art. Waxes which have a relatively high oilcontent and are, therefore, relatively plastic and soft, such as slackwaxes, are preferably extruded in the solid form rather than ejectedinto the cooling fluid in the liquid state. By operating in this mannerthe necessity for melting the wax for transferring to the sweater iseliminated. Waxes which have a relatively low oil content, such as scalewaxes, are preferably melted and formed into pellets by ejection of themolten wax as small globules into a stream of cooling fluid. Due to thelow oil content of these waxes, they are less plastic and, therefore,more readily assume a permanent shape than plastic waxes whensolidified. Whether the crude wax to be sweated is pelleted from aliquid or a solid state depends upon the nature of the wax beingprocessed.

In order to avoid agglomeration of the globules or pellets of theejected wax, it is desirable to eject the wax vertically upward and tohave the same flow concurrently with the cooling fluid. The ejectingmeans is of a sufficiently large diameter so as to minimize turbulenceand is long enough to insure complete solidification of the outersurface of the pellet before it reaches a line of a reduced diameter. Byoperating in this manner, the wax globules will not become concentratedin the upper part of the pipe, as they would were the pipe placed inhorizontal position. Agglomeration and plugging of the equip- 1 ment arethus avoided. It is also extremely desirable to adjust the temperatureof the molten wax so that it is ejected into the cooling fluid only afew degrees above its melting point in order to avoid undue delay in thesolidification period. In general, the temperature of a liquid wax as itis ejected into the cooling fluid should be less than 5 above itsmelting point and preferably less than 3 above its melting point.

Any suitable inert cooling fluid may be used as a cooling medium.However, in general, the cooling fluid preferably comprises water.

In order further to illustrate the invention, the following examples aregiven which should not be construed as limiting the same in any mannerwhatsoever. In various operations, a slack wax of about 107 F. meltingpoint, containing about 26% of oil, was prepared in three forms andcharged to a sweater pan. All forms were sweated for crude scale wax.The results of these operations were as follows:

Method of charging sweater pan Conven- Extruded tional, i. e., waxpellets gi sf g f molten wax of about Sion of ax allowed 34" dia. charto solidify charged to i in pan to pan p Temp. at start of opern. F 7578 Sweater yields:

Foots oil, vol. percent of charge to pan 35 26 20 Intermediate slackwax, vol. percent of charge to pan 25 33 54 Crude scale wax, vol.percent of charge to pan.-. 4O 41 26 Oil in crude scale wax percent.. 22. 2 1 4 Melting point of crude scale wax F- 120 1 120 1 Above. 9 Below.

From the above it is apparent that the pelleted wax of the presentinvention sweats as satisfactorily as does wax charged in theconventional manner to the pan. It is also apparent that the size of thewax particles is critical in order to V avoid emulsiflcation and poorsweating.

The invention may be adapted to all present conventional forms ofsweating crude petroleum waxes for the purpose of separating oil andwax. It may be readily adapted to charge both the tank and pan type ofsweater.

The invention is not to be limited by any theory or mode of operationbut only in and by the following claims in which it is desired to claimall novelty in so far as the prior art permits.

I claim:

1. Improved process for sweating crude solid waxes comprising extrudingthe same into a cooling fluid under conditions to secure relativelysmall solid wax particles, passing the fluid containing the solid waxparticles to a sweating pan, withdrawing the cooling fluid and thensubject: ing the wax particles to gradually increasing temperatures.

2. Process as defined by claim 1 in which said particles have a diameterin the range from about to inch, and in which said cooling fluidcomprises water.

3. Improved process for sweating crude solid waxes comprising meltingthe same, ejecting the melted wax into a cooling fluid under conditionsto secure solid relatively small wax particles, passing the fluidcontaining the wax particles to a sweating pan, withdrawing the coolingfluid and then subjecting the wax particles to gradually increasingtemperatures.

4. Process as defined by claim 3 in which said wax particles have adiameter in the range from about to A inch, and in which said coolingfluid comprises water.

5. Process as defined by claim 3 in which said melted wax is injectedupwardly into upflowing cooling fluid comprising water.

HAROLD J. MOYER.

